The present invention relates to an air/fuel ratio sensor for detecting the air/fuel ratio of an air and fuel mixture supplied to an engine and more particularly to an air/fuel ratio sensor including an oxide ion-conducting solid electrolyte.
An air/fuel ratio sensor, which measures the oxygen concentration in the exhaust discharge, is generally incorporated in an engine so as to improve the fuel consumption rate and emission. One type of well-known air/fuel ratio sensors includes an electrochemical pump cell (oxygen pump cell; Ip) and an electrochemical sensor cell (oxygen concentration cell; Vs) facing each other with a gas diffusion chamber in between, and a gas diffusion hole connecting the gas diffusion chamber to the outside.
Recently, various attempts have been made to improve the performance of the sensor in an atmosphere including substantially no oxides, e.g., N.sub.2 --O.sub.2 dry air.
Japanese Published Unexamined patent application No. Sho-61-147155 has disclosed an improved sensor, which shows a stable limiting current in the Ip-Vs relation. The primary feature of the sensor is that the sizes- of the electrode on the gas diffusion chamber side and of the diffusion chamber are respectively adjusted within a specified range.
Japanese Published Unexamined patent application No. Sho-61-221644 has proposed another improved sensor, which has two electrodes of identical size and exhibits a quick response.
The above sensors, however, still have some problems. Though the first sensor shows a stable limiting current even in dry air, it does not exhibit a sufficiently quick response. The second sensor shows a stable limiting current only in an atmosphere including neutral oxides such as H.sub.2 O and CO.sub.2, but not in dry air including substantially no oxides.
Wherefore, the object of the invention is thus to provide an air/fuel ratio sensor with a quick response; but, which shows a stable limiting current even in an atmosphere including substantially no oxides.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.